Steam and air boiler with heating surface of smallest load



Oct. 10, 1961 P. BOCK ETAL 3,003,479

STEAM AND AIR BOILER WITH HEATING SURFACE OF SMALLEST LOAD Filed Oct. 8.19s: 2 Sheets-Sheet 1 CONVECTION SUPERHEATER H IN S I ENERA G URFACEECONOMlZER NATURAL CIRCULATION VAPOR GENERATOR INVENTORS. PETER BOCKHANS SPIES KARL DEITLHAUSER Oct. 10, 1961 P. BOCK ETAL 3,003,479

STEAM AND AIR BOILER WITH HEATING SURFACE OF SMALLEST LOAD Filed Oct. 8,1953 2 Sheets- Sheet 2 INVENTORS. 4 PETER BOCK HANS SPIES BY KARLDEITLHAUSER ATTORNEY United States Patent "3 cc v 1 3,003,479 STEAM ANDAIR BOILER WITH HEATING SURFACE OF SMALLEST LOAD Peter Bock, Hans Spies,and Karl Deitlhauser, Ratingen,

Rhineland, Germany, assignors to Durrwerke Aktiengesellschaft, Rafingen,Germany, a corporation of Ger- Filed Oct. 8, 1953, Ser. No. 384,978Claims priority, application Germany Oct. 11, 1952 3 Claims. (Cl. 122-4)The subject of the invention is a steam and air boiler of a type whichpermits operation at the smallest load demanded of the unit.

In the construction of power plants, for reasons of economy, preferenceis given more and more to unit power plants, that is, the constructionof one turbine with one or two boilers serving it. At Starting up of theunit power plants, it is desirable to adapt the steam generation to thelimited steam demanded for warming up the turbines. This smallest loadis about five percent (%)v of the maximum load and is considerably underthe usual values.

To meetsuch low load, prior art units have had to operate at higher loadand throw away the excess. This excess was condensed in the startingcondensers and by this a great part of the produced heat was eliminatedinto the cooling water.

The smallest load of five percent (5%) is so low that it creates unsafefio-w instability problems which preclude the use of a conventionalboiler for such purposes. People tried to avoid these difficulties byerecting a special starting boiler, but because of its limitedutilization the starting boiler was too expensive.

To meet the demands expected from the unit power plants and avoid thementioned disadvantages, the invention proposes to arrange a smallestload furnace in one part of the heating surface of the boiler which istouched by the flue gases of the main furnace, this part of the heatingsurface is partly or totally connected in parallel to the remaining partof the boiler.

The advantage of the construction of the invention, lies in the factthat a smallest load can be handled without additional heating surfaces.This smallest load portion provides a unit capable of lower loads thanother units have reached to date. Thus, at starting, the steamgeneration is adapted to the. steam demand of the turbine and water lossand heatloss have been avoided. Moreover, now it will be possible to.feed the connected turbine in the unit with no-load steam during thewarming up period or on stand-by.

The invention will now be described, by way of example, with referenceto the accompanying diagrammatic drawings in which:

FIGURE 1 illustrates a forced flow once-through boilerfcr steam or airin agreement with the invention;

FIGURE 2 illustrates a natural circulation boiler;

FIGURE 3 'is a semi-schematic vertical side view of a unit as shown inFIGURE 2; and

FIGURE 4 is a plan view of the unit of FIGURE 3 at the line 4r-.

In FIGURE '1 of the drawings, number 1 marks the feed water pumpwherefrom the water is pumped through the shut ofif valve 2 andconducted to the single flow boiler consisting of the economizer 3, theradiation heat and steam generating surface 4, the transition heatingsurface 5, the radiation superheater 6 and the convection superheater 7.The generated steam streams through the shut-off valve 8 to the turbine9. The starting line 10 with shut-off valve 11 serves for starting theboiler.

The minimum load furnace is shown at 6 and in FIG- URBS 1 and 2 servesfor heating the radiation super- 3,003,479 Patented'Oct. 10, 1961 heaterpart 6a and the following convection superheater part 7a. The dimensionsof these smallest load heating surfaces 6a and 7a connected in parallelto the single flow boilerare adapted to the smallest load as desired.

The, mode "of operation of the just described single flow boiler used assteam generator is as follows when starting:

When the singlefiow boiler consisting of the heating surfaces 3 to 7 isfilledwith water, water is pumped through the line 12 through thesmallest load heating surface 6a and 7a and discharged through thestarting line with valve 15. The valve 8 is closed and valve 18regulates the quantity of vaporizable liquid that flows through thesmallest load heating sections'fia and 7a. The quantity of the fed waternearly corresponds to the desired smallest load. Then the smallest loadfurnace 16 is put into operation and arranged in such a manner that thegenerated steam reaches the temperature of superheated steam necessaryto heat the turbine. With valve 15 you can position the wanted pressure.By opening valve 14 and correspondingly closing valve 15, the steamnecessary for heating is lead to turbine 9.

When the turbine is ready to deliver load, the single flow boiler 3 to 7is started by the starting line fitted with valve 11 and when thedesired value of the steam is reached also connected to the turbine 9 byopening valve Sand correspondingly closing valve 11. By this, the mainfurnace of the single flow boiler also heats the smallest load heatingsurface 6a and 7a. The smallest load furnace therefore mustcorrespondingly be reduced and then cut off. In case the endtemperatures of the single flow boiler should notexactly harmonize theshare of water quantity can be regulated by moving valve 13 while valve2 is open. Feed water regulation valve 17 serves for the totalregulation of the water.

In the natural circulation boiler in FIGURE 2, the drum is completelyfilled during the work with smallest load of the heating surfaces 6::and 7a; the water flows through the drum. During .thistime, valve 24 isclosed. When the operation with the smallest load is finished, the drumis emptied to the normal water level through valve 25. Valve 24 is.opened and the boiler is started in the same way as the usual'naturalcirculation boiler.

FIGS. 3 and 4 illustrate"semi-schematically a vapor generating andsuperheating unit constructed according to the diagram of FIG. 2 inwhich case the small load heating portion (6a and 7a) is arranged inparallel with the main radiant heated superheater 6 and convectionsuperheater 7. The arrangement of this unit may be best understood bydescribing the operation of the unit. Nor- 'mally, feed water is sent tothe unit by the feed pump 1 into the econornizer section'3 which extendsacross the entire width of a convection heating gas pass. The heatedwater then passes into radiant heated water cooled sections 4 which linethe walls of the lower portion of aradiant furnace chamber.

These sections are arranged as vertical panels in which the heatedliquid rises to the top of the panel and then is conducted by unheateddowncomers, as indicated by thejarrows, to an adjacent panel where theliquid again flows upwardly and eventually the heated liquid, which ispartially vaporized, passes into the transformation heating surface 5where the liquid is completely converted to steam. The transformationheating surface extends across the entire width of the convection pass.Upon leaving the transformation heating surface 5, a branch linecontaining a valve 18 conducts a part of the steam to the smallest loadradiant heated portion 6a while the main bulk of steam goes to theparallel flowing superheater 7. The superheater 6a is arranged in theupper part of the furnace chamber as tube panels (shown dotted) in whichthe tubes are in line as platens, on either side to form a spacetherebetween wherein a small load furnace chamber is formed and intowhich a special burner 16 may be fired to create hot gases for start-uppurposes. These hot gases give up heat only to the panel sections 6abefore 'leaving the furnace chamber and pass into the downpass as itflows over the convection superheater 7a. This fiuid which is heated insection 6a passes over into the section 7a before passing out througheither valve 14 on the way to the turbine 9 or valve 14 to an exhaustsystem. In normal operation of the vapor generating and superheatingunit' illustrated, valves 8, 14 and 18 are open so that the small loadheating portion operates in parallel as a normal portion of thesuperheater of the unit; however, when it is desired to start-up theunit valve 8 of the main superheater section is closed so that the onlycooling fluid flow is through the economizer, radiant heated section 4,transformation section and the small load superheater sections 6a and7a. The burner 16 is tired to create the hot gases and the small amountof vaporizable liquid flowing is heated, vaporized and superheated inthe sections 6a and 7a in such a way to be completely independent fromthe rest of the steam generating unit. The refractory division walls 26on either side of the convection supenheater portion 7a assure that thehot gases leaving the furnace, heat only the convection superheater.Thus, there is shown a small load heating section integral with aonce-through vapor generator yet arranged such that it may be fired andheated independent from the rest of the steam generator.

In accordance with the invention, the smallest load heating surface canbe formed by each other part of the heating surface. At any rate thekind of the smallest load heating surface is determined by theconstruction of the boiler or its furnace.

The smallest load furnace can be separated according to ones liking bythe walls of the tubes or by refractory material. An especially suitableseparation is possible when a superheater is arranged which is formed bywalls of tubes and the smallest load furnace is placed between two ofsuch adjoining walls of tubes.

A by-pass may be arranged it the flue gases of the smallest load furnaceare not wanted to stream through the succeeding heating surfaces.

We claim:

1. A vapor generating and superheating unit comprising wall meansforming a gas flow chamber; economizer, vapor generating and vaporsuperheating sections disposed in said chamber; a start-up minimum loadportion including said economizer section and parts of the vaporgenerating section and of the vapor superheating section; saideconomizer section and said parts of the vapor generating section and ofthe vapor superheating section being connected for serial flow of fluidtherethrough; means connecting said minimum load portion in parallelflow relation with the remaining parts of said vapor generating sectionand said vapor super-heating section; first combustion means supplyinghigh temperature gases to said chamber to normally heat said sections;said minimum load portion being of a size to provide the minimum loadvapor requirements for said unit; means for flowing all of thevaporizable fluid supplied for start-up through said minimum loadportion to generate superheated vapor therein during the start-up of theunit; and second combustion means arranged to fire only said minimumload portion during start-up.

2. A vapor generating and superheating unit comprising wall meansforming a gas flow chamber; economizer, vapor generating and vaporsuperheating sections disposed in said chamber; a start-up minimum loadportion including said economizer section and parts of the vaporgenerating section and of the vapor 'superheating section; saideconomizer section and said parts of the vapor generating section and ofthe vapor superheating section being connected for serial flow of fluidtherethrough; means connecting said load portion in parallel flowrelation with the remaining parts of said vapor generating section andsaid vapor superheating section; first combustion means supplying hightemperature gases to said chamber to normally heat said sections; saidload portion being of a size to provide the minimum load vaporrequirements for said unit; means for flowing all of the vaporizablefluid supplied for start-up through said minimum load portion togenerate superheated vapor therein during the start-up of the unit; andsecond combustion means arranged to fire only said load portion duringstart-up; said minimum load portion having at least a part of its vaporsuperheating section arranged to form radiant heat receiving walls. 7 Y

3. A vapor generating and superheating unit comprising wall meansforming a gas flow chamber; economizer, vapor generating and vaporsuperheating sections disposed in said chamber; a start-up minimum loadportion including said economizer section and parts of the vaporgenerating section and of the vapor superheating section; saideconomizer section and said parts of the vapor genera-ting section andof the vapor superheating section being connected for serial flow offluid therethrough; means connecting said minimum load portion inparallel flow relation with the remaining parts of said vapor generatingsection and said vapor superheating section; first combustion meanssupplying high temperature gases to said chamber to normally heat saidsections; said minimum load portion being of a size to provide theminimum load vapor requirements for said unit; means for flowing all ofthe vaporizable fluid supplied for start-up through said minimum loadportion to generate superheated vapor therein during the start-up of theunit; and second combustion means arranged to fire only said minimumload portion during start-up; said minimum load portion having at leasta part of its vapor superheatin-g section arranged to form radiant heatreceiving walls and comprising two laterally spaced panels of tubes withcombustion of fuel from Said second combustion means occurringtherebetween.

References Cited in the file of this patent UNITED STATES PATENTS

